This invention relates to structural wall systems employed in the construction of commercial and industrial buildings and more particularly concerns on-site construction of concrete wall panels incorporating insulating materials in the panel.
The basic principle of incorporating an insulating material between two layers of concrete is not unique to the construction industry. However, efforts to utilize this principle in a practical wall system with sufficient flexibility to encompass a wide range of commercial and industrial applications have met with limited success. The insulated concrete wall panel systems currently marketed are generally inadequate due to deficient insulating properties, excessive bulk and weight characteristics, structural complexity or a combination of these design inadequacies.
They consist basically of two structurally independent concrete panels with a layer of insulation material between them in order to achieve both structural and insulation properties. In this arrangement, the addition of a second layer of concrete, insulation material, steel reinforcing materials and the connectors necessary for lamination to the primary layer of concrete produce a heavy and difficult to handle panel. Panels of this type often weigh in excess of 100 pounds per square foot of panel area. The mechanical connection of two heavy, independent concrete panels with an insulation layer between them presents structural problems which are difficult to overcome. Furthermore, the insulation thickness which can be incorporated between the concrete layers without compounding the structural problems is limited.
Other disadvantages result because the insulation material in these systems generally covers the entire area of the "primary" panel, leaving the edges of the insulation material exposed in the finished product. This allows penetration of moisture between the two layers of concrete causing corrosion in the laminating tie system, decay of the insulation material, loss of insulation properties and eventual structural problems.
A variation of this multi-panel, laminate design substitutes a concrete "grid" or "waffle" pattern slab on top of a self-sufficient primary panel with insulation panels occurring within the concrete grid. This variation eliminates the problem of exposed insulation edges and structural bonding problems between the separate concrete panels, but the overall panel weight is extremely high. Therefore, as with the previously described panel configuration, this inefficient design results in high cost and a cumbersome product to handle, transport and erect.
Despite the fact that these panels are heavy and cumbersome, the normal procedure is to construct them in an off-site facility and then transport them to the job-site for erection. They could be constructed on-site but additional problems of control are added to those of design, resulting in a finished product of haphazard quality and undependable structural capability. Furthermore, the entire building project is delayed until all the wall panels have been formed and poured on the building floor slab and allowed to "cure" for a period of perhaps ten to twenty days. This period of project "shutdown" during fabrication of the wall panels can consume from six weeks to three months, depending upon the scope of the project.
In another variation directed at these on-site problems, wall panels utilizing the laminate principle have been constructed on the job-site in a vertical position directly over the footing system. But this requires highly labor intensive form systems and an on-site assembled steel reinforcing structure. Of all presently used insulated wall systems, this is the most labor intensive, time consuming and expensive. Walls of this type are "custom built" without any of the benefits of production techniques and systems. It is also difficult to place concrete into the formed wall system without dislodging the insulation material occurring at the central point of the wall.
It is therefore an object of this invention to facilitate a versatile concrete wall panel system utilizing the compositelaminate principle that is capable of supporting structural loads commonly encountered in commercial and industrial buildings, but which can be readily produced in volume at a competitive cost. Another object of this invention facilitates construction of a concrete wall panel system which combines both structural and insulating functions in a single, monolithic system without duplication of function. Similarly, it is an object of this invention to facilitate construction of a concrete wall panel system which completely surrounds the insulation components in the reinforced monolithic, concrete body of the panel, providing both the structural requirements and protective facing for the insulation material in a strong, lightweight product.
Moreover, it is an object of this invention to provide a preattached form system for a concrete wall panel in which the form members which define the perimeter of the panel are rigidly connected to the panel reinforcing members. And it is a further object of this invention to provide a pre-attached form system which permit the rigid connection thereto of any insulation supports, lifting anchors, weld plates and other accessories in condition ready for the addition of insulation panels and concrete material either on or off-site.
One advantage of this invention is to reduce on-site panel construction time to approximately two to three days. The light weight of a panel formed by this system allows manipulation of the panel with a significantly smaller mobile crane than would otherwise be required.
Greater accuracy in forming is achieved, resulting in superior dimensional tolerances for the panel. This also results in a reduction in the erection time required. A higher panel quality is achieved, with known structural and insulation characteristics. Accurate panel dimensions and location of weld plates and other accessories is assured. It is not necessary to rigidly attach forming members to the floor slab of the building, eliminating the need to install and remove fasteners and patch the resulting holes. Panels can be easily "stack-cast" if sufficient, unobstructed floor space is not available. In this process, one panel is poured directly on top of another. Stacking of panels of conventional job-cast design results in substantially higher forming costs. The job-site labor force is significantly reduced. The pre-fabricated perimeter form design could also be readily used in a remote site operation, eliminating the need for expensive steel form beds and concrete placement equipment.